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Physiographic features, Trans-Pecos region
James R. Underwood Jr., 1980, pp. 57-58
in:
Trans Pecos Region (West Texas), Dickerson, P. W.; Hoffer, J. M.; Callender, J. F.; [eds.], New Mexico Geological
Society 31st Annual Fall Field Conference Guidebook, 308 p.
This is one of many related papers that were included in the 1980 NMGS Fall Field Conference Guidebook.
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New Mexico Geological Society Guidebook, 31st Field Conference, Trans-Pecos Region, 1980
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PHYSIOGRAPHIC FEATURES, TRANS-PECOS REGION
JAMES R. UNDERWOOD, JR.
Department of Geology
Kansas State University
Manhattan, Kansas 66506
The summit of Eagle Peak, 2,285 m above sea level, the highest
point in Hudspeth County and the eighth highest peak in Texas, affords an unexcelled view of vast parts of Trans-Pecos Texas and
northern Chihuahua, Mexico.
The Indio Mountains, which extend southward from the Eagle
Mountains to the Rio Grande, are composed largely of marine
strata of Cretaceous age. Tertiary volcanic rocks cover a large area
in the southern part of the mountains; intrusive rocks are
volumetrically minor and occur only in the northern Indios.
North- to northwest-trending thrust faults are prominent in Devil
Ridge and in the Indio Mountains. The southwestward and westward movement of the overthrust block along some of the faults
in the Indio Mountains is opposite to the northeastward movement of the overthrust blocks along the faults in the Devil Ridge
area. Late Tertiary normal faulting and subsequent erosion are
responsible for the present topography.
To the north, Guadalupe Peak, the highest point in Texas with an
elevation above sea level of 2,668 m, and El Capitan, only 152 m
lower, are both remnants of the massive Permian Capitan barrier
reef that bordered the Delaware Basin. These lofty limestone
masses provide the background for the Diablo Plateau, which
stretches away to the north and northwest at an elevation of 1,525
to 1,830 m, and separates Hueco Bolson to the west from Salt
Basin to the east. Sierra Diablo, a north-trending range along the
eastern margin of the Diablo Plateau, overlooks Salt Basin to the
east and contains the most nearly complete rock record in the
region. In these mountains, rocks ranging in age from Precambrian
through Cretaceous, except those of Cambrian, Triassic, and Jurassic age, are well exposed. Northwest of Sierra Diablo is a distinctive rocky and angular peak, Sierra Prieta (Black Mountain), composed of porphyritic alkalic igneous rock, that rises a thousand feet
above the Diablo Plateau.
Salt Basin is a remarkably smooth-floored depression more than
160 km long, averaging 32 km wide, into which water drains from
all directions. This closed basin, the easternmost of those of the
Basin and Range province, is a long, narrow north-trending halfgraben, bordered on the west by the Sierra Diablo and on the east
by the Delaware and Apache Mountains, which compose the distant northeast skyline.
The Delaware Mountains are an elongate north-northwesttrending fault block in which Permian sandstone and shale of the
Delaware Basin facies have been uplifted and exposed. In contrast,
the Apache Mountains are an exposed northwest-trending part of
the ancient Capitan barrier reef. The sharp notch in the northeast
skyline is Seven Heart Gap, a pass between the Delaware and the
Apache Mountains.
Much nearer and just north of Van Horn are the Beach and Baylor Mountains, relatively small fault blocks composed largely of
rocks of Precambrian, Ordovician, and Permian age. Just west of
Van Horn and bordering Eagle Flat on the northeast are the Carrizo
Mountains in which metamorphosed sedimentary and volcanic
rocks of Precambrian age predominate. Bass Canyon, marked by
the well-defined depression in the profile of the southern Carrizo
Mountains, is the pass through which an old stage road runs,
which in the mid-nineteenth century connected San Antonio and
San Diego.
The broad, flat lowland just west of the Carrizo Mountains and
immediately north of the Eagles is Eagle Flat, the drainage of which
flows southeastward into Salt Basin through a water gap between
the Carrizo and Van Horn Mountains.
The eastern skyline is formed by the Davis Mountains, a vast Tertiary volcanic field of alkalic igneous rocks. The sharp, triangular
summit of Mt. Livermore, the jagged silhouette of Sawtooth, and
the rugged north-facing prominence of Gomez Peak are all distinctive features, even at a distance of 80 to 95 km from Eagle Peak.
In the foreground, dividing the southern end of Salt Basin into
Michigan Flat on the east and Lobo Flat on the west, are the Wylie
Mountains, a horst block composed largely of Permian and Cretaceous rocks. Just south of the main block of the Wylies, the Three
Sisters (three small buttes of volcanic rock), Canning Ridge (quartz
monzonite intrusion), and Chispa Peak (composed of volcanic
rock) are prominent features along the east margin of Lobo Flat.
Just beyond Green River to the east and southeast are the Van
Horn Mountains in which High Lonesome, elevation 1,714 m
above sea level, is the high volcanic rock mass at the north end.
On the distant southeastern skyline, displaying a distinctive angular silhouette, is Sierra Vieja, or the Rim Rock Mountains, composed of a sequence of Tertiary flow and pyroclastic rocks. Still farther south and east and plainly visible on clear days are the Chinati
Mountains near Ruidosa, Texas, some 120 km away.
The view southward into Chihuahua is no less impressive. In this
region the Rio Grande, in its path toward the Gulf of Mexico,
wanders alternately through broad open valleys and deep, steepwalled canyons cut into rugged highlands. South of the Indio
Mountains, beyond where the Rio Grande cuts through the range,
are, in order, the Sierra Pilares, Sierra Ventana, Sierra de la Parra,
and Sierra Grande. This range, which extends 160 km south-southeastward to the vicinity of Ojinaga, Chihuahua, is composed
largely of folded Cretaceous rocks.
Far to the south, west of the southern Sierra Pilares and Sierra de
Ventana, is Bolson del Cuervo. Just west, in succession are the
northwest-trending Sierra del Alambre and the high Sierra del Pino,
which compose the distant southwest skyline. In the near foreground and extending northward to the Rio Grande is the Sierra de
la Cieneguilla, a low range of overturned Cretaceous rocks. The
Quitman Mountains make the peculiarly uneven skyline to the
west and northwest. Folded and thrust-faulted Cretaceous rocks
compose the southern part of the mountains, and Tertiary intrusive and flow rocks make up most of the northern Quitmans.
The low point of the skyline is Quitman Gap, the canyon that
separates the two segments of the range. The old stage road went
through this pass and on west about 14 km to Fort Quitman, near
the Rio Grande.
Just north of the Quitmans and near the western margin of the
Diablo Plateau is easily the most distinctive feature of this panorama. Sierra Blanca, "White Mountain," a laccolith of light-colored
intrusive rock with convex slopes sweeping gracefully to a summit
2,134 m above sea level, is a magnificent landmark.
UNDERWOOD
58
sedimentary rocks intruded by Tertiary alkalic igneous rocks similar to those in the Hueco Mountains. Also to the north-northwest
but much nearer are the Pump Station Hills—low, rounded, poorly
exposed outcrops of red rhyolite porphyry of Precambrian age.
This geologically spectacular region thus exposes a rock record
that spans more than a billion years of earth history and that varies
from the scattered exposures of the very old Texas craton to the
alluvium that was deposited by the most recent flood of the Rio
Grande.
The Malone and Finlay Mountains, low ranges farther west and
northwest on the western margin of the Diablo Plateau, contain
gently folded rocks, largely of Permian and Cretaceous age. The
Malone Mountains contain the only outcrop in Texas of marine
strata of Jurassic age.
The Hueco and Cornudas Mountains, some 80 to 95 km northwest and north-northwest, respectively, are relatively low-lying
masses that extend northward into New Mexico. The Hueco
Mountains, along the northwest margin of the Diablo Plateau and
the east margin of the Hueco Bolson, is a barren range composed
primarily of sedimentary rocks of Paleozoic age. Along the
southern margin of the mountains there are scattered small outcrops of red granite which have been assigned a Precambrian age;
to the north near the state line there are Tertiary alkalic intrusive
rocks. Hueco Tanks, an old Indian campsite and later a station on
the Butterfield stage route, are natural rock cisterns in low knobs
of these intrusive rocks.
The Cornudas Mountains, some 32 km east of the Huecos and
also along the New Mexico border, are composed of Cretaceous
ACKNOWLEDGMENT
Appreciation is expressed to the Permian Basin Section of the
Society of Economic Paleontologists and Mineralogists for permission to use this material, first published in SEPM Permian Basin Section Guidebook 75-15, Geology of the Eagle Mountains and Vicinity, Trans-Pecos Texas, and taken in part from University of TexasAustin Ph.D. dissertation in geology (Underwood, 1962) supervised by Ronald K. DeFord.
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GUADALUPE
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SIERRAQ
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Figure 1. Physiographic sketch of Trans-Pecos Texas and northern Chihuahua, based on Coas
and Geodetic Survey, El Paso Sectional Aeronautical Chart, 1965 (courtesy of D. H. Campbell).
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